Highway snow and ice control typically is carried out by governmental authorities with the use of dump trucks which are seasonally modified by the addition of snow-ice treatment components. These components will include a forwardly-mounted plow and rearwardly-mounted mechanisms for broadcasting materials such as salt-aggregate mixtures. Such mechanisms conventionally include a feed auger extending across the back edge of the dump bed of the truck. This hydraulically driven auger effects a metered movement of material from the bed of the truck onto a rotating spreader disk or "spinner" which broadcasts or spreads the salt or salt-aggregate mixture across the pavement being treated.
In snow-ice control procedures heretofore undertaken, salt containing materials are spread during snow-ice build-up on interstate or principal highways at a rate of about 600 lbs per mile as a first or initial application. Secondary highways are treated at deposition rates of about 400 lbs per mile for such an initial application. Thereafter, the salt carrying trucks may follow-up with a reapplication of the selected treatment material at deposition rates of about 200 lbs per mile.
The speed of the snow-ice control vehicles necessarily is constrained during inclement weather conditions to about 15 miles per hour. This lower speed permits the broadcasting of salt-aggregate materials without undue loss to roadside regions. Additionally, the inclement conditions will generally cause traveling motorists to lower average speeds on the highway such that the slow, 15 mph trucks do not pose a severe slow moving hazard. Environmentalists have expressed concern with respect to the quantity of salt-based materials distributed into run-off channels by this treatment procedure. This concern has developed to an extent that investigators are looking for procedures which remain effective in snow-ice control while lessening the amount of control materials which must be used. One improvement in the controlled deposition of these materials has been achieved through the utilization of microprocessor driven controls over the hydraulics employed with the seasonally modified trucks. Kime, et al., in U.S. Pat. No. Re.33,835 entitled "Hydraulic System for Use with Snow-Ice Removal Vehicles", reissued Mar. 3, 1992, describe a microprocessor driven hydraulic system for such trucks with a provision for digital hydraulic valving control which is responsive to the instantaneous speed of the truck. With the hydraulic system, improved controls over the extent of deposition of snow-ice materials is achieved. This patent is expressly incorporated herein by reference.
Other techniques for improving snow-ice control have looked to selection of the timing of controlled material deposition. For example, the amount of material required for initial deposition can be reduced significantly where it is laid down prior to the commencement of storm generated precipitation. By so pre-treating highways, a brine is formed at the pavement surface at the onset of precipitation which prevents ice from bonding to the pavement surface. Additionally, this "pre-treating" procedure facilitates the removal of accumulated snow-ice by plowing procedures. By laying down the material, for example an hour before the commencement of storm precipitation, the amount of material required for an initial application may be, for example, 1/6th of that required after precipitation has commenced and snow-ice build-up is present on the highway. While such pre-treatment may be effective, the problem now becomes one of the technique of depositing it properly upon the highway surface. Snow-ice materials, utilized in conventional equipment, will remain on the highway surface at the time of deposition only where the depositing vehicles are traveling at dangerously slow speeds for dry pavement, for example, about 15 miles per hour. Above those slow speeds, the material is essentially lost to the roadside. Observation of materials attempted to be deposited at higher speeds shows the aggregates bouncing forwardly, upwardly, and being broadcast over the pavement sides such that the deposition at higher speeds is ineffective as well as dangerous and potentially damaging to approaching vehicles. However, the depositing trucks themselves constitute a serious hazard when traveling, for example at 15 mph, on dry pavement which simultaneously is accommodating vehicles traveling, for example at 65 mph. The danger posed is such as to preclude the practicality of pre-treating deposition. A practical technique is called for which controls the deposition of snow-ice materials while permitting the trucks to operate at those higher speeds which are reasonably safe with respect to approaching traffic on major interstate highways.